`f(x) = 4/(x^2 + 1)`

`or, f(x) = 4*(x^2 + 1)^-1`

`thus, f'(x) = -4*(2x)*(x^2 +1)^-2`

`or, f'(x) = -8x/(x^2 +1)^2`

`or, f'(-1) = (-8*-1)/{(-1)^2 + 1}^2`

`or, f'(x) = 8/4 = 2`

``

`f(x) = 4/(x^2 + 1)`

`or, f(x) = 4*(x^2 + 1)^-1`

`thus, f'(x) = -4*(2x)*(x^2 +1)^-2`

`or, f'(x) = -8x/(x^2 +1)^2`

`or, f'(-1) = (-8*-1)/{(-1)^2 + 1}^2`

`or, f'(x) = 8/4 = 2`

``